Resin composition and resin molded article

ABSTRACT

A resin composition includes a thermoplastic resin, a carbon fiber, a polyamide having at least one of a carboxy group and an amino group at a terminal thereof, in which a presence ratio of the carboxy group present on the terminal is higher than a presence ratio of the amino group present on the terminal, and a compatibilizer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2016-248099 filed Dec. 21, 2016.

BACKGROUND 1. Technical Field

The present invention relates to a resin composition and a resin moldedarticle.

2. Related Art

In the related art, various resin compositions are provided and are usedfor various applications.

In particular, resin compositions containing a thermoplastic resin areused in various components and housings of home electronics andautomobiles or are used in various components such as housings ofbusiness machines and electric and electronic apparatuses.

SUMMARY

According to an aspect of the invention, there is provided a resincomposition including:

a thermoplastic resin;

a carbon fiber;

a polyamide having at least one of a carboxy group and an amino group ata terminal thereof, in which a presence ratio of the carboxy grouppresent on the terminal (terminal carboxy group) is higher than apresence ratio of the amino group present the terminal (terminal aminogroup); and

a compatibilizer.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described indetail based on the following figures, wherein:

FIG. 1 is a model diagram showing major parts of a resin molded articleaccording to an exemplary embodiment; and

FIG. 2 is a schematic diagram for describing an example of the majorparts of the resin molded article according to the exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment which is an example of a resincomposition and a resin molded article according to an exemplaryembodiment of the invention will be described.

Resin Composition

The resin composition according to the exemplary embodiment includes athermoplastic resin, a carbon fiber, a polyamide, and a compatibilizer.

In recent years, in order to obtain a resin molded article superior inmechanical strength, particularly bending elastic modulus, a resincomposition containing a thermoplastic resin as a matrix and areinforcing fiber has been used.

In the resin composition, when affinity between the reinforcing fiberand the thermoplastic resin is low, a space is formed at an interfacetherebetween, and adhesion at the interface may deteriorate.

In particular, in a case where a carbon fiber is used as the reinforcingfiber in the resin composition, it is required to have higher mechanicalstrength, particularly bending elastic modulus than that of glass fiber.However, since the number of the polar group contributing to adhesion tothe thermoplastic resin such as hydroxyl group and carboxy group on thesurface of the carbon fiber is smaller than that of the polar group ofthe glass fiber, the adhesion at the interface between the carbon fiberand the thermoplastic resin deteriorates. As a result, the mechanicalstrength, particularly the bending elastic modulus is unlikely enhancedin spite of the formulation of carbon fibers. In particular, in a casewhere impact is applied repeatedly, flaking easily proceeds at theinterface between the carbon fiber and the thermoplastic resin, so thatthe mechanical strength, particularly bending elastic modulus tends tobe largely deteriorated.

Therefore, the resin composition according to the exemplary embodimentincludes four components: the thermoplastic resin, the polyamide, thecarbon fiber, and the compatibilizer.

By adopting this configuration, for example, a resin molded articlesuperior in mechanical strength, particularly bending elastic modulusmay be obtained as compared with a case where only a thermoplastic resinand carbon fiber are contained.

Here, when forming the resin molded article, for example, fluidity ofthe resin composition may be low in some cases since a viscosity of athermally melted resin composition is too high. In a case where thefluidity of the thermally melted resin composition is low, moldabilityof the resin composition is lowered, for example, the accuracy of theshape of the intended resin molded article is lowered, and thedimensional accuracy of the resin molded article may be lowered in somecases.

On the other hand, the resin composition according to the exemplaryembodiment contains at least one of a carboxy group and an amino groupat a terminal as the polyamide, in addition to the above fourcomponents, and a resin having a higher presence ratio of the terminalcarboxy group than that of the terminal amino group is applied. That is,the polyamide is a resin having at least one of a carboxy group and anamino group at the terminal, and having a higher ratio of the carboxygroup than that of the amino group with respect to the carboxy group orthe amino group that may exist at both terminals. The polyamide having ahigher presence ratio of the terminal carboxy group than that of theterminal amino group may have the carboxy groups at both terminals.

In the present specification, the terminal amino group refers to anamino group present at the terminal of the polyamide, and the terminalcarboxy group refers to the carboxy group present at the terminal of thepolyamide.

By adopting this configuration, a resin composition superior in fluiditymay be obtained. By molding using the resin composition superior influidity, a resin molded article superior in dimensional accuracy may beobtained. Although the action of obtaining such an effect is not clear,it is presumed as follows.

Since the polyamide has a high presence ratio of the terminal carboxygroup, the polyamide is likely to be decomposed by heating and themolecular weight is likely to decrease. As a result, it is consideredthat since the viscosity of the resin composition when heated and melteddecreases, the fluidity of the resin composition when forming the resinmolded article is enhanced. By molding using a resin composition withenhanced fluidity, it is considered that the resin molded articlesuperior in dimensional accuracy may be obtained since the resincomposition is likely to be filled in the mold.

From the above, with respect to the resin composition according to theexemplary embodiment, it is presumed that since the ratio of the carboxygroup present at the terminal of the polyamide is high, the viscosity ofthe resin composition when heated and melted decreases and the fluidityis improved. In addition, it is presumed that the resin molded articlesuperior in dimensional accuracy may be obtained by using the resincomposition superior in fluidity.

When the resin composition according to the exemplary embodimentincludes the above four components, the resultant molded article issuperior in mechanical strength, particularly bending elastic modulus,as compared with, for example, a case where only the thermoplastic resinand the carbon fiber are included. Although the action of obtaining suchan effect is not clear, it is considered as follows.

When the resin composition is thermally molten-kneaded in order toobtain the resin molded article from the resin composition according tothe exemplary embodiment, the thermoplastic resin as the matrix and thecompatibilizer are melted, and a part of the molecules of thecompatibilizer and the amide bond contained in the molecules of thepolyamide are compatibilized. As a result, the polyamide is dispersed inthe resin composition.

In this state, when the polyamide contacts the carbon fiber, the amidebond contained in a large number along the molecular chain of thepolyamide and a polar group slightly present on a surface of the carbonfiber are physically bonded to each other through affinity (attractionand hydrogen bond) at plural sites. In addition, generally, thecompatibility between the thermoplastic resin and the polyamide is low.Therefore, due to repulsion between the thermoplastic resin and thepolyamide, the contact frequency between the polyamide and the carbonfiber increases. As a result, the amount or area of the polyamide bondedto the carbon fiber increases. In this manner, using the polyamide, thecoating layer is formed around the carbon fiber (refer to FIG. 1). InFIG. 1, PP represents the thermoplastic resin, CF represents the carbonfiber, and CL represents the coating layer.

Since the polyamide forming the coating layer is also compatible byperforming the chemical reaction with a part of the reactive groups inthe molecule of the compatibilizer and electrostatic interaction betweenthe polar groups, the compatibilizer is compatible with thethermoplastic resin. Therefore, an equilibrium state is formed betweenattraction and repulsion, and the coating layer of the polyamide isformed in a thin and substantially uniform state. In particular, theaffinity between a carboxy group present on a surface of the carbonfiber and the amide bond contained in the molecules of the polyamide ishigh. Therefore, it is presumed that the coating layer is easily formedaround the carbon fiber using the polyamide, and the coating layer isthin and has superior uniformity.

The coating layer preferably coats the entire circumference of thecarbon fiber, while there maybe a portion which is not partially coated.

As described above, in the resin composition according to the exemplaryembodiment, the adhesion of the interface between the carbon fiber andthe thermoplastic resin is enhanced. As a result, it is considered thatthe resin molded article obtained from the resin composition accordingto the exemplary embodiment is superior in mechanical strength,particularly bending elastic modulus, as compared with, for example, acase where only the thermoplastic resin and carbon fiber are included.

The resin composition according to the exemplary embodiment and theresin molded article obtained may have a structure in which a coatinglayer of a polyamide is formed around the carbon fiber by heatmolten-kneading and injection molding for preparing of the resincomposition (for example, pellet), and the thickness of the coatinglayer is from 5 nm to 700 nm.

In the resin composition according to the exemplary embodiment, thethickness of the coating layer of the polyamide may be from 5 nm to 700nm, and is preferably from 10 nm to 650 nm from the viewpoint of furtherimproving the bending elastic modulus. When the thickness of the coatinglayer is set to 5 nm or more (especially 10 nm or more), the bendingelastic modulus is improved. When the thickness of the coating layer isset to 700 nm or less, the interface between the carbon fiber and thethermoplastic resin via the coating layer is prevented from beingweakened, and the deterioration in the bending elastic modulus isprevented.

The thickness of the coating layer is a value measured using thefollowing method. A measurement target is cut in liquid nitrogen, and across-section thereof is observed using an electron microscope (VE-9800,manufactured by Keyence Corporation). In the cross-section, thethickness of the coating layer which is formed around the carbon fiberis measured at 100 positions, and the average value thereof is obtained.

The coating layer is determined by observing the above cross-section.

In the resin composition (and the resin molded article thereof)according to the exemplary embodiment, for example, the compatibilizeris configured to be partially compatible with the coating layer and thethermoplastic resin.

Specifically, for example, a layer of the compatibilizer may beinterposed between the coating layer of the polyamide and thethermoplastic resin as the matrix (refer to FIG. 2). That is, the layerof the compatibilizer is formed on the surface of the coating layer, andthe coating layer and the thermoplastic resin may be adjacent to eachother via the layer of the compatibilizer. Although the layer of thecompatibilizer is formed to be thinner than the coating layer, theadhesion (bonding property) between the coating layer and thethermoplastic resin is enhanced by the interposition of the layer of thecompatibilizer, and the resin molded article superior in mechanicalstrength, particularly bending elastic modulus, is easily obtained. InFIG. 2, PP represents the thermoplastic resin, CF represents the carbonfiber, CL represents the coating layer, and CA represents the layer ofthe compatibilizer.

In particular, the layer of the compatibilizer is bonded to the coatinglayer (hydrogen bond, covalent bond by reaction of the functional groupbetween the compatibilizer and the polyamide, and the like), and thethermoplastic resin may be interposed between the coating layer and thethermoplastic resin in a state of being compatible with thethermoplastic resin. This configuration is easily achieved, for example,when the compatibilizer has the same structure as or compatiblestructure with the thermoplastic resin as the matrix, and thecompatibilizer containing a site reactive with a functional group of theabove-described polyamide is applied to a part of the molecule.

Specifically, for example, in a case where a polyolefin thermoplasticresin, polyamide, and a compatibilizer for maleic anhydride modifiedpolyolefin are applied, in the layer of the maleic anhydride modifiedpolyolefin (layer of compatibilizer), the carboxy group formed byring-opened of the maleic anhydride site reacts with and binds to theamine residue of the polyamide layer (coating layer), and the polyolefinsite thereof may be interposed in a state of being compatible with thepolyolefin.

Here, a method for checking that the layer of the compatibilizer isinterposed between the coating layer and the thermoplastic resin is asfollows.

As an analyzer, a microscopic infrared spectroscopic analyzer(manufactured by JASCO Cooperation, IRT-5200) is used. For example, asliced piece is cut out from the resin molded article includingpolypropylene (hereinafter referred to as PP) as the thermoplasticresin, PA 66 having a high presence ratio of the terminal carboxy groupsas a specific resin, and maleic acid-modified polypropylene (hereinafterreferred to as MA-PP) as a modified polyolefin, and a cross-sectionthereof is observed. IR mapping of the coating layer around thecross-section of the carbon fiber is performed to confirm maleicanhydride (1820 cm⁻¹ to 1750 cm⁻¹) derived from the coatinglayer-compatibilized layer. As a result, it may be confirmed that thelayer of the compatibilizer (binding layer) is interposed between thecoating layer and the thermoplastic resin.

Hereinafter, the details of each component of the resin compositionaccording to the exemplary embodiment will be described.

Thermoplastic Resin (A)

The thermoplastic resin is the matrix of the resin composition and aresin component which is reinforced by the carbon fiber (also referredto as “matrix resin”).

The thermoplastic resin is not particularly limited, and examplesthereof include polyolefin (PO), polyphenylene sulfide (PPS), polyamide(PA), polyimide (PI), polyamide imide (PAI), polyether imide (PEI),polyether ether ketone (PEEK), polyether sulfone (PES), polyphenylsulfone (PPSU), polysulfone (PSF), polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polyacetal (POM), polycarbonate (PC),polyvinylidene fluoride (PVDF), acrylonitrile-butadiene-styrenecopolymers (ABS), and acrylonitrile styrene (AS).

One type of thermoplastic resin may be used alone, or two or more typesmay be used in combination.

Among these, polyolefin (PO) is preferable from the viewpoints offurther improving bending elastic modulus and reducing the cost.

Polyolefin is a resin containing a repeating unit derived from an olefinand may contain another repeating unit derived from a monomer other thanolefin as long as polyolefin is 30% by weight or less with respect tothe total weight of the resin.

Polyolefin is obtained by addition polymerization of olefin (optionally,the monomer other than olefin).

In addition, regarding each of the olefin and the monomer other thanolefin for obtaining polyolefin, one type may be used alone, or two ormore types may be used in combination.

The polyolefin may be a copolymer or a homopolymer. In addition, thepolyolefin may be linear or branched.

Examples of the olefin described herein include linear or branchedaliphatic olefins and alicyclic olefins.

Examples of the aliphatic olefins include α-olefins such as ethylene,propylene, 1-butene, 1-hexene, 4-methyl-l-pentene, 1-octene, 1-decene,1-hexadecene, and 1-octadecene.

In addition, examples of the alicyclic olefins include cyclopentene,cycloheptene, norbornene, 5-methyl-2-norbornene, tetracyclododecene, andvinylcyclohexane.

Among these, from the viewpoint of reducing the cost, α-olefin ispreferable, ethylene or propylene is more preferable, and propylene isstill more preferable.

In addition, the monomer other than olefin is selected from well-knownaddition-polymerizable compounds.

Examples of the addition-polymerizable compounds include: styrenes suchas styrene, methylstyrene, α-methylstyrene, β-methylstyrene,t-butylstyrene, chlorostyrene, chloromethylstyrene, methoxystyrene,styrenesulfonic acid, and salts thereof; (meth) acrylates such as alkyl(meth)acrylate, benzyl (meth)acrylate, and dimethylaminoethyl(meth)acrylate; halovinyls such as vinyl chloride; vinyl esters such asvinyl acetate and vinyl propionate; vinyl ethers such as vinyl methylether; vinylidene halides such as vinylidene chloride; and N-vinylcompounds such as N-vinylpyrrolidone.

Preferable examples of polyolefin include polypropylene (PP),polyethylene (PE), polybutene, polyisobutylene, coumarone-indene resin,terpene resin, ethylene-vinyl acetate copolymer resin (EVA), and thelike.

Among these, the resin containing only the repeating unit derived fromolefin is preferable. In particular, from the viewpoint of reducing thecost, polypropylene is preferable.

The molecular weight of the thermoplastic resin is not particularlylimited, and may be determined according to the type of resin, moldingconditions, and the use of the resin molded article. For example, whenthe thermoplastic resin is the polyolefin, the weight average molecularweight (Mw) thereof is preferably in a range of 10,000 to 300,000 andmore preferably in a range of 10,000 to 200,000.

As in the case of the molecular weight, the glass transition temperature(Tg) or melting point (Tm) of the thermoplastic resin is notparticularly limited, and may be determined according to the type of theresin, molding conditions, and the use of the resin molded article. Forexample, when the thermoplastic resin is polyolefin, the melting point(Tm) thereof is preferably in a range of 100° C. to 300° C., and morepreferably in a range of 150° C. to 250° C.

The weight average molecular weight (Mw) and melting point (Tm) ofpolyolefin are a value measured using the following method.

That is, the weight average molecular weight (Mw) of polyolefin ismeasured by gel permeation chromatography (GPC) under the followingconditions. As a GPC system, a high-temperature GPC system “HLC-8321GPC/HT” is used. As an eluent, o-dichlorobenzene is used. Polyolefin isdissolved in o-dichlorobenzene at a high temperature (140° C. to 150°C.), and the solution is filtered to obtain the filtrate as ameasurement sample. The measurement is performed using an RI detectorunder the following measurement conditions of sample concentration:0.5%, flow rate: 0.6 ml/min, and sample injection amount: 10 μl. Inaddition, a calibration curve is prepared from 10 samples, “PolystyleneStandard Sample TSK Standard”: “A-500”, “F-1”, “F-10”, “F-80”, “F-380”,“A-2500”, “F-4”, “F-40”, “F-128”, and “F-700” (manufactured by TosohCorporation).

In addition, the melting point (Tm) of polyolefin is calculated from theDSC curve obtained from differential scanning calorimetry (DSC)according to a “melting peak temperature” described in a method ofcalculating melting temperature in “Testing methods for transitiontemperatures of plastics” of JIS K7121-1987.

The content of the thermoplastic resin as the matrix may be determinedaccording to, for example, the use of the resin molded article. Forexample, the content of the thermoplastic resin is preferably from 5% byweight to 95% by weight, more preferably from 10% by weight to 95% byweight, and still more preferably from 20% by weight to 95% by weightwith respect to the total weight of the resin composition.

In a case where the polyolefin is used as the thermoplastic resin, thecontent of polyolefin is preferably 20% by weight or higher with respectto the total weight of the thermoplastic resin.

Carbon Fiber

As the carbon fiber, a well-known carbon fiber is used, and any one of aPAN carbon fiber and a pitch carbon fiber is used.

The carbon fiber may undergo a well-known surface treatment.

Examples of the surface treatment for the carbon fiber include anoxidation treatment and a sizing treatment.

The form of the carbon fiber is not particularly limited, and may beselected according to the use of the resin molded article. Examples ofthe form of the carbon fiber include a fiber bundle including a largenumber of single fibers, a bundled fiber bundle, and a woven fabric inwhich fibers are two-dimensionally or three-dimensionally woven.

The fiber diameter, the fiber length, and the like of the carbon fiberare not particularly limited, and may be selected according to the useof the resin molded article.

Here, even if the fiber length of the carbon fiber is short, since theresin molded article superior in mechanical strength, particularlybending elastic modulus may be obtained, the average fiber length of thecarbon fibers may be from 0.1 mm or about 0.1 mm to 5.0 mm or about 5.0mm (preferably from 0.2 mm to 2.0 mm).

In addition, the average diameter of the carbon fibers may be, forexample, from 5.0 μm to 10.0 μm (preferably from 6.0 μm to 8.0 μm).

Here, the measurement method of the average fiber length of the carbonfibers is as follows. The carbon fiber is observed with an opticalmicroscope at a magnification of 100 times to measure the length of thecarbon fiber. The measurement is performed for 200 carbon fibers, andthe average value thereof is taken as the average fiber length of thecarbon fibers.

On the other hand, the measurement method of the average diameter ofcarbon fibers is as follows. A cross-section perpendicular to thelongitudinal direction of the carbon fiber is observed with a scanningelectron microscope (SEM) at a magnification of 1,000 times to measurethe diameter of the carbon fiber. The measurement is performed for 100carbon fibers, and the average value thereof is taken as the averagediameter of the carbon fibers.

When the fiber length of the carbon fiber is shortened, the resinreinforcing capacity of the carbon fiber tends to deteriorate. Inparticular, due to recent demands for recycling, it is also promoted topulverize and recycle the resin molded article reinforced with thecarbon fiber, and the fiber length of the carbon fiber is shortenedduring pulverizing the resin molded article. In addition, the fiberlength of the carbon fiber is short during heat molten-kneading whenpreparing the resin composition in some cases. Therefore, when the resinmolded article is molded from the resin composition containing thecarbon fiber whose fiber length is shortened, the mechanical strength,particularly the bending elastic modulus, tends to be deteriorated.

However, even when the resin molded article containing the carbon fiberis pulverized, recycled product in which the carbon fiber is convertedto the short fiber is used as a raw material, or the carbon fiber isconverted to the short fiber during heat molten-kneading, the resincomposition according to the exemplary embodiment is useful because theresin molded article superior in mechanical strength, particularlybending elastic modulus may be obtained.

As the carbon fiber, a commercially available product may be used.

Examples of a commercially available product of the PAN carbon fiberinclude “TORAYCA” (registered trade name; manufactured by TorayIndustries Inc.), “TENAX” (manufactured by Toho Tenax Co., Ltd.) , and“PYROFIL” (registered trade name; manufactured by Mitsubishi Rayon Co.,Ltd.). Other examples of a commercially available product of the PANcarbon fiber include commercially available products manufactured byHexcel Corporation, Cytec Industries Inc., Dow-Aksa, Formosa PlasticsGroup, and SGL Carbon Japan Co., Ltd.

Examples of a commercially available product of the pitch carbon fiberinclude “DYAD” (registered trade name; manufactured by Mitsubishi RayonCo., Ltd.), “GRANOC” (manufactured by Nippon Graphite Fiber Co., Ltd.),and “KUREKA” (manufactured by Kureha Corporation). Other examples of acommercially available product of the pitch carbon fiber includecommercially available products manufactured by Osaka Gas Chemical Co.,Ltd., and Cytec Industries Inc.

One type of carbon fiber may be used alone, or two or more types may beused in combination.

The content of the carbon fiber is preferably from 0.1 parts or about0.1 parts by weight to 200 parts or about 200 parts by weight, morepreferably from 1 part by weight to 180 parts by weight, and still morepreferably from 5 parts by weight to 150 parts by weight with respect to100 parts by weight of the thermoplastic resin.

By adjusting the content of the carbon fiber to be 0.1 parts by weightor more with respect to 100 parts by weight of the thermoplastic resin,the resin composition is reinforced. In addition, by adjusting thecontent of the carbon fiber to be 200 parts or about 200 parts by weightor less with respect to 100 parts by weight of the thermoplastic resin,the moldability during the preparation of the resin molded article issuperior.

In a case where the reinforcing fiber other than the carbon fiber isused, the carbon fiber may be used in an amount of 80% by weight orhigher with respect to the total weight of the reinforcing fiber.

Hereinafter, the content (part(s) by weight) with respect to 100 partsby weight of the thermoplastic resin will be abbreviated as “phr (perhundred resin)” in some cases.

In a case where this abbreviation is used, the content of the carbonfiber is from 0.1 phr to 200 phr.

Polyamide

The polyamide contains a specific partial structure and is a resin thatmay coat around the carbon fiber as described above. In addition, thepolyamide has at least one of a carboxy group and an amino group at theterminal, and has a higher ratio of the terminal carboxy group than thatof the terminal amino group (hereinafter, simply referred to as“presence ratio of the terminal carboxy group is high”).

The polyamide will be described in detail.

The polyamide may be a resin having a low compatibility with thethermoplastic resin, and specifically, a resin having a solubilityparameter (SP value) different from the solubility parameter of thethermoplastic resin.

Here, the difference between the SP value of the thermoplastic resin andthe SP value of the polyamide may be 3 or more and more preferably from3 to 6 from the viewpoints of compatibility therebetween and repulsiontherebetween.

The SP value is a value calculated according to Fedor's method.Specifically, the solubility parameter (SP value) may be calculated, forexample, using the following expression according to the description ofPolym. Eng. Sci., vol. 14, p. 147 (1974).

Expression:

SP Value=√(Ev/v)=√(ΣΔei/ΣΔvi)

(Here, Ev: evaporation energy (cal/mol), v: molar volume (cm³/mol), Δei:evaporation energy of each of atoms or an atomic group, ΔAvi: molarvolume of each of atoms or an atomic group) (cal/cm³)^(1/2) is adoptedfor the unit of the solubility parameter (SP values). However, the unitwill be omitted in accordance with customs, and the SP values will berepresented in a dimensionless form.

In addition, the polyamide contains an amide bond in the moleculesthereof.

By containing the amide bond, the polyamide exhibits affinity to a polargroup present on a surface of the carbon fiber.

Since the presence ratio of the terminal carboxy group of the polyamideis high, the fluidity of the resin composition when heated is enhanced.

For example, in the case where the polyamide is a mixture of two or moretypes having different concentrations of the terminal carboxy group, thepresence ratio of the carboxy group in the polyamide as the total of thepolyamides may be high.

Here, the fluidity of the resin composition is evaluated by measuringthe MFR of the resin composition. The MFR of the resin composition ismeasured under the conditions that a temperature is 270° C. and a loadis 2.16 kg according to JIS K 7210-1 (2014). That is, MFR is a numericalvalue representing the fluidity at the time of resin melting, and isobtained by measuring the amount of a resin extruded per 10 minutesthrough a die having a prescribed diameter set at the bottom of acylinder in which the resin is melted under the above conditions(temperature and load).

From the viewpoint of improving the fluidity of the resin composition,the presence ratio of the terminal carboxy group of the polyamide maysatisfy the following conditions as a ratio of the terminal carboxygroup concentration based on the total of the terminal amino groupconcentration and the terminal carboxy group concentration.

0.5<[B]/([A]+[B])≤1.0

[A]: concentration of the terminal amino group concentration per 1 kg ofthe polyamide (mol/kg)

[B]: concentration of the terminal carboxy group concentration per 1 kgof the polyamide (mol/kg)

In addition, from the viewpoint of further improving the fluidity of theresin composition, it is preferable to satisfy the condition0.6≤[B]/([A]+[B]≤1.0, and it is more preferable to satisfy the condition0.7≤[B]/([A]+[B])≤1.0.

The concentration of the carboxy group present at the terminal (terminalcarboxy group concentration) of the polyamide may be, for example, 0.01(mol/kg) or more and 0.50 (mol/kg) or less (preferably 0.02 (mol/kg) ormore and 0.40 (mol/kg) or less).

The terminal amino group concentration and the terminal carboxy groupconcentration of the polyamide are measured as follows.

After dissolving the resin in an N-methyl-2-pyrrolidone solvent, theterminal amino group concentration (mol/kg) causes an excess amount oftrifluoroacetic anhydride to act on the terminal amino group togetherwith a triethylamine catalyst. After removing the resin byreprecipitation, the amount of fluorine atom present in the resin isdetermined by F-NMR, the amount of terminal amino group is calculated,and the terminal amino group concentration is determined.

After dissolving the resin in an N-methyl-2-pyrrolidone solvent, theterminal carboxy group concentration (mol/kg) causes an excess amount oftrifluoroethanol and di-t-butyl carbodiimide to act on the terminalcarboxy group together with a pyridine catalyst. After removing theresin by reprecipitation, the amount of fluorine atom present in theresin is determined by F-NMR, the amount of terminal carboxy group iscalculated, and the terminal carboxy group concentration is determined.

[B]/([A]+[B]) is calculated from the values of the obtained terminalamino group concentration and terminal carboxy group concentration.

In a case where two or more types of the polyamide are used incombination, the ratio of the terminal amino group concentration basedon the total of the terminal amino group concentration and the terminalcarboxy group concentration per 1 kg of the combined polyamide isdetermined.

Examples of the polyamide having high presence ratio of the terminalcarboxy group include a polyamide obtained by co-polycondensing adicarboxylic acid and a diamine, a polyamide obtained by condensing adicarboxylic acid and a lactam, and a polyamide obtained by condensing adicarboxylic acid, a diamine, and a lactam. That is, as the polyamide, apolyamide having at least one of a structural unit in which adicarboxylic acid and a diamine are condensation-polymerized, and astructural unit in which a lactam is ring-opened may be exemplified.

A polyamide having a high presence ratio of the terminal carboxy groupmay be obtained, for example, by performing condensation reaction usinga dicarboxylic acid component in an excess amount relative to othercomponents for synthesizing a polyamide. For example, the dicarboxylicacid component may be used in such an amount that the ratio of theterminal carboxy group concentration based on the total of the terminalamino group concentration and the terminal carboxy group concentrationper 1 kg of the polyamide is a target value.

The polyamide may be a polyamide having a structural unit in which adicarboxylic acid and a diamine are condensation-polymerized, apolyamide having a structural unit in which lactam is ring-opened, andeither a structural unit containing an aromatic ring excluding aramid ora structural unit not containing the aromatic ring, or a polyamidehaving a structural unit containing the aromatic ring excluding anaramid structural unit and a structural unit not containing the aromaticring, as long as the presence ratio of the terminal carboxy group ishigher. From the viewpoint of the bending elastic modulus, the polyamidemaybe a polyamide having the structural unit containing the aromaticring excluding the aramid structural unit and the structural unit notcontaining the aromatic ring.

In particular, when the polyamide having the structural unit containingthe aromatic ring excluding the aramid structural unit and thestructural unit not containing the aromatic ring is applied as thepolyamide having a high presence ratio of the terminal carboxy group,the affinity between the carbon fiber and the thermoplastic resin isimproved. Here, polyamide having only the structural unit containing thearomatic ring tends to have higher affinity with the carbon fiber andlower affinity with the thermoplastic resin than polyamide having onlythe structural unit not containing the aromatic ring. The polyamidehaving only the structural unit not containing the aromatic ring tendsto have the lower affinity with the carbon fiber and the higher affinitywith the thermoplastic resin than the polyamide having only thestructural unit containing the aromatic ring. Therefore, by applying thepolyamide having both structural units, the affinity with both of thecarbon fiber and the thermoplastic resin is improved, and the adhesionat the interface between the carbon fiber and the thermoplastic resin isfurther enhanced by the coating layer of the polyamide. Therefore, it iseasy to obtain the resin molded article superior in mechanical strength,particularly bending elastic modulus.

In addition, when the polyamide having the structural unit containingthe aromatic ring excluding the aramid structural unit and thestructural unit not containing the aromatic ring is used as thepolyamide having a high presence ratio of the terminal carboxy group,the melt viscosity deteriorates and the moldability (for example,injection moldability) also improves. Therefore, the resin moldedarticle having high appearance quality is easily obtained.

When polyamide having only aramid structural unit is applied as theabove polyamide, thermal degradation of the thermoplastic resin iscaused at high temperatures at which the polyamide may melt. Inaddition, at a temperature at which thermal degradation of thethermoplastic resin is caused, the polyamide may not be sufficientlymelted, the moldability (for example, injection moldability) isdeteriorated, and the appearance quality and the mechanical performanceof the obtained resin molded article are deteriorated.

The aromatic ring means a monocyclic aromatic ring (cyclopentadiene andbenzene) having 5-membered or more rings, and a condensed ring(naphthalene, and the like) condensed with plural monocyclic aromaticrings having 5-membered or more rings. The aromatic ring also includes aheterocyclic ring (pyridine, and the like).

In addition, “aramid structural unit” refers to a structural unitobtained by polycondensation reaction between dicarboxylic acidcontaining the aromatic ring and diamine containing the aromatic ring.

Here, examples of the structural unit containing an aromatic ringexcluding the aramid structural unit include at least one of thefollowing structural units (1) and (2).

Structural unit (1): —(—NH—Ar¹—NH—CO-R¹—CO—)—

(In the structural unit (1), Ar¹ represents a divalent organic groupcontaining an aromatic ring. R¹ represents a divalent organic group notcontaining the aromatic ring.)

Structural unit (2): —(—NH-R²—NH—CO—Ar²—CO—)—

(In the structural unit (2), Ar² represents a divalent organic groupcontaining the aromatic ring. R² represents a divalent organic group notcontaining the aromatic ring.)

On the other hand, examples of the structural unit not containing anaromatic ring include at least one of the following structural units (3)and (4).

Structural unit (3): —(—NH-R³¹—NH—CO-R³²—O—)—

(In the structural unit (3), R³¹ represents a divalent organic group notcontaining the aromatic ring. R³² represents a divalent organic groupnot containing the aromatic ring.)

Structural unit (4): —(—NH-R⁴—CO—)—

(In the structural unit (4), R⁴ represents a divalent organic group notcontaining the aromatic ring.)

In formulas (1) to (3), the “divalent organic group” represented by eachsymbol is an organic group derived from a divalent organic grouppossessed by dicarboxylic acid, diamine, or lactam. Specifically, forexample, in the structural unit (1), “divalent organic group containingthe aromatic ring” represented by Ar¹ represents a residue obtained byremoving two amino groups from diamine, and “divalent organic group notcontaining the aromatic ring” represented by R¹ represents a residueobtained by removing two carboxy groups from dicarboxylic acid. Inaddition, for example, in the structural unit (4), “divalent organicgroup not containing the aromatic ring” represented by R⁴ is an organicgroup interposed between “NH group” and “CO group” when the lactam isring-opened.

As the polyamide, any of a copolymerized polyamide and a mixed polyamidemay be used as long as the presence ratio of the terminal carboxy groupis high. As the polyamide, the copolymerized polyamide and the mixedpolyamide may be used in combination. Among these, the mixed polyamideis preferable as the polyamide from the viewpoint of further improvingthe mechanical strength, particularly bending elastic modulus.

In the aromatic polyamide, the ratio of the structural unit containingan aromatic ring is preferably 80% by weight or more (preferably 90% byweight or more, and more preferably 100% by weight or more) based on thewhole structural units.

On the other hand, in the aliphatic polyamide, the ratio of thestructural unit not containing the aromatic ring is preferably 80% byweight or more (preferably 90% by weight or more, and more preferably100% by weight or more) based on the whole structural units.

Examples of the aromatic polyamide include a condensation polymer ofdicarboxylic acid containing the aromatic ring and diamine notcontaining the aromatic ring, and a condensation polymer of dicarboxylicacid not containing the aromatic ring and diamine containing thearomatic ring.

Examples of the aliphatic polyamide include a condensation polymer ofdicarboxylic acid not containing the aromatic ring and diamine notcontaining the aromatic ring, and the like. A ring-opened polycondensateof lactam not containing the aromatic ring, and the like may beincluded.

Here, examples of the dicarboxylic acid containing the aromatic ringinclude phthalic acid (terephthalic acid, isophthalic acid, and thelike), biphenyldicarboxylic acid, and the like.

Examples of the dicarboxylic acid not containing the aromatic ringinclude oxalic acid, adipic acid, suberic acid, sebacic acid,1,4-cyclohexanedicarboxylic acid, malonic acid, succinic acid, glutaricacid, pimelic acid, azelaic acid, and the like.

Examples of the diamine containing the aromatic ring includep-phenylenediamine, m-phenylenediamine, m-xylenediamine,diaminodiphenylmethane, diaminodiphenyl ether, and the like.

Examples of the diamine not containing the aromatic ring includeethylenediamine, pentamethylenediamine, hexamethylenediamine,nonanediamine, decamethylenediamine, 1,4-cyclohexanediamine, and thelike.

Examples of the lactam not containing the aromatic ring includeϵ-caprolactam, undecane lactam, lauryl lactam, and the like.

Each dicarboxylic acid, each diamine, and each lactam may be used aloneor two or more types may be used in combination.

As the aromatic polyamide, for example, a polyamide having a skeletonsuch as MXD 6 (condensation polymer of adipic acid and metaxylenediamine), nylon 6T (condensation polymer of terephthalic acid andhexamethylenediamine), nylon 6I (polycondensate of isophthalic acid andhexamethylenediamine), nylon 9T (polycondensate of terephthalic acid andnonanediamine), and nylon M5T (polycondensate of terephthalic acid andmethylpentadiamine), and having a high presence ratio of the terminalcarboxy groups present at the terminal of these polyamides is included.

As the aliphatic polyamide, for example, a polyamide having a skeletonsuch as nylon 6 (ring-opened polycondensate of ϵ-caprolactam), nylon 11(ring-opened polycondensate of undecane lactam), nylon 12 (ring-openedpolycondensate of lauryllactam), nylon 66 (condensation polymer ofadipic acid and hexamethylenediamine), and nylon 610 (condensationpolymer of sebacic acid and hexamethylenediamine), and having a highpresence ratio of the terminal carboxy groups present at the terminal ofthese polyamides is included.

Physical properties of the polyamide will be described.

The molecular weight of the polyamide is not particularly limited, andthe molecular weight may be as long as the polyamide is likely to bethermally melted than the thermoplastic resin coexisting in the resincomposition. For example, the weight average molecular weight of thepolyamide is preferably in the range of 10,000 to 300,000, and morepreferably in the range of 10,000 to 100,000.

In addition, a glass transition temperature or a melting temperature(melting point) of the polyamide is not particularly limited, similar tothe above molecular weight, and the temperature may be as long as thepolyamide is likely to be thermally melted than the thermoplastic resincoexisting in the resin composition. For example, the melting point (Tm)of polyamide (each polyamide of copolymerized polyamide and mixedpolyamide) is preferably in the range of 100° C. to 400° C., and morepreferably in the range of 150° C. to 350° C.

From the viewpoint of further improving the mechanical strength,particularly bending elastic modulus, the content of the polyamide ispreferably 0.1 parts by weight or more and 100 parts by weight or less,more preferably 0.5 parts by weight or more and 90 parts by weight orless, and further preferably 1 part by weight or more and 80 parts byweight or less based on 100 parts by weight of the thermoplastic resin.

When the content of the polyamide is within the above range, theaffinity with the carbon fiber is enhanced and the mechanical strength,particularly the bending elastic modulus is improved.

In particular, when the polyamide is included in a large amount in arange of exceeding 20 parts by weight and 100 parts by weight or lessbased on 100 parts by weight of the thermoplastic resin, the amount ofthe compatibilizer becomes relatively small to the amount of thepolyamide, the polyamide becomes difficult to spread in thethermoplastic resin, and the tendency to localize around the carbonfibers is enhanced. As a result, it is considered that the coating layerof polyamide is formed in a state close to uniformity while thickeningto some extent over the entire circumference of the carbon fiber havinga short fiber length. Therefore, the adhesion of the interface betweenthe carbon fiber and the thermoplastic resin is enhanced, and a resinmolded article superior in mechanical strength, particularly bendingelastic modulus, is likely to be obtained.

From the viewpoint of effectively exhibiting the affinity with thecarbon fiber, the content of the polyamide maybe proportional to thecontent of the carbon fiber described above.

The content of the polyamide based on the weight of the carbon fiber ispreferably 0.1% or about 0.1% by weight or more and 200% or about 200%by weight or less, more preferably 1% by weight or more and 150% byweight or less, and further preferably 1% by weight or more and 120% byweight or less.

When the content of the polyamide based on the weight of the carbonfiber is 0.1% by weight or more, the affinity between the carbon fiberand the polyamide is likely to be increased, and when the content is200% by weight or less, the resin flowability is improved.

Compatibilizer

The compatibilizer is a resin that enhances the affinity between thethermoplastic resin and the polyamide.

The compatibilizer may be determined according to the thermoplasticresin.

The compatibilizer may have the same structure as the thermoplasticresin and contains a portion having affinity to the polyamide in a partof the molecules.

For example, in a case where polyolefin is used as the thermoplasticresin, modified polyolefin may be used as the compatibilizer.

Here, when the thermoplastic resin is polypropylene (PP), modifiedpolypropylene (PP) is preferable as the modified polyolefin. Likewise,when the thermoplastic resin is an ethylene-vinyl acetate copolymerresin (EVA), a modified ethylene-vinyl acetate copolymer resin (EVA) ispreferable as the modified polyolefin.

Examples of the modified polyolefin include polyolefins into which amodification site containing a carboxy group, a carboxylic anhydrideresidue, a carboxylate residue, an imino group, an amino group, an epoxygroup, or the like is introduced.

From the viewpoints of further improving the affinity between thepolyolefin and the polyamide and considering the upper limit temperatureduring molding, the modification site to be introduced into thepolyolefin preferably contains a carboxylic anhydride residue, and inparticular, more preferably contains a maleic anhydride residue.

The modified polyolefin may be obtained using, for example, a method ofcausing a compound containing the above-described modification site toreact with polyolefin such that the modification site is directlychemically bonded to polyolefin or a method of forming a graft chainusing a compound containing the above-described modification site andbonding the graft chain to polyolefin.

Examples of the compound containing the above-described modificationsite include maleic anhydride, fumaric anhydride, citric anhydride,N-phenylmaleimide, N-cyclohexylmaleimide, glycidyl (meth)acrylate,glycidyl vinylbenzoate,N-[4-(2,3-epoxypropoxy)-3,5-dimethylbenzyl]acrylamide, alkyl(meth)acrylate, and derivatives thereof.

In particular, modified polyolefin obtained by causing a reactionbetween maleic anhydride as an unsaturated carboxylic acid to react withpolyolefin is preferable.

Specific examples of the modified polyolefin include acid-modifiedpolyolefins such as maleic anhydride-modified polypropylene, maleicanhydride-modified polyethylene, a maleic anhydride-modifiedethylene-vinyl acetate copolymer resin (EVA), and adducts or copolymersthereof.

As the modified polyolefin, a commercially available product may beused.

Examples of the modified propylene include YOUMEX (registered tradename) series (100TS, 110TS, 1001, 1010) manufactured by Sanyo ChemicalIndustries, Ltd.

Examples of the modified polyethylene include YOUMEX (registered tradename) series (2000) manufactured by Sanyo Chemical Industries, Ltd. andMODIC (registered trade name) series manufactured by Mitsubishi ChemicalCorporation.

The molecular weight of the compatibilizer is not particularly limitedand, from the viewpoint of workability, is preferably from 5,000 to100,000 and more preferably 5,000 to 80,000.

The content of the compatibilizer is preferably from 0.1 parts by weightto 50 parts by weight, more preferably from 0.1 parts by weight to 40parts by weight, and still more preferably from 0.1 parts by weight to30 parts by weight with respect to 100 parts by weight of thethermoplastic resin.

The content of the compatibilizer is preferably from 1 part or about 1part by weight to 50 parts or about 50 parts by weight, more preferablyfrom 5 parts by weight to 50 parts by weight, and still more preferablyfrom 10 parts by weight to 50 parts by weight with respect to 100 partsby weight of the polyamide.

By adjusting the content of the compatibilizer to be within theabove-described range, the affinity between the thermoplastic resin andthe polyamide is enhanced, and the mechanical strength, particularly thebending elastic modulus may be improved.

From the viewpoint of enhancing the affinity between the thermoplasticresin and the polyamide, it is preferable that the content of thecompatibilizer may be proportional to the content of the polyamide (isindirectly proportional to the content of the carbon fiber).

The content of the compatibilizer is preferably from 1% by weight to 50%by weight, more preferably from 1% by weight to 40% by weight, and stillmore preferably from 1% by weight to 30% by weight with respect to theweight of the carbon fiber.

When the content of the compatibilizer is 1% by weight or higher withrespect to the weight of the carbon fiber, the affinity between thecarbon fiber and the polyamide is likely to be obtained. When thecontent of the compatibilizer is 50% by weight or lower (in particular,30% by weight or lower), the remaining of an unreacted functional groupcaused by discoloration or deterioration is prevented.

Other Components

The resin composition according to the exemplary embodiment may containother components in addition to the above-described components.

Examples of the other components include well-known additives such as aflame retardant, a flame retardant auxiliary agent, a dripping inhibitorduring heating, a plasticizer, an antioxidant, a release agent, a lightresistant agent, a weather resistant agent, a colorant, a pigment, amodifier, an antistatic agent, a hydrolysis inhibitor, a filler, and areinforcing agent other than the carbon fiber (for example, talc, clay,mica, glass flake, milled glass, glass beads, crystalline silica,alumina, silicon nitride, aluminum nitride, or boron nitride).

The content of the other components is preferably from 0 part by weightto 10 parts by weight and more preferably from 0 part by weight to 5parts by weight with respect to 100 parts by weight of the thermoplasticresin. Here, “0 part by weight” represents that the resin compositiondoes not contain other components.

Method of Preparing Resin Composition

The resin composition according to the exemplary embodiment is preparedby molten-kneading the respective components.

Here, a well-known unit is used as a molten-kneading unit, and examplesthereof include a twin-screw extruder, a HENSCHEL MIXER, a BUNBURYMIXER, a single-screw extruder, a multi-screw extruder, and aco-kneader.

The temperature (cylinder temperature) during molten-kneading may bedetermined according to, for example, the melting point of the resincomponents constituting the resin composition.

In particular, the resin composition according to the exemplaryembodiment may be obtained using a preparing method includingmolten-kneading the thermoplastic resin, the carbon fiber, thepolyamide, and the compatibilizer. When the thermoplastic resin, thecarbon fiber, the polyamide, and the compatibilizer are collectivelymolten-kneaded, the coating layer which is formed around the carbonfiber using the polyamide is likely to be formed in a thin andsubstantially uniform state, and the mechanical strength, particularlythe bending elastic modulus, is enhanced.

Resin Molded Article

The resin molded article according to the exemplary embodiment containsthe thermoplastic resin, the carbon fiber, the polyamide, and thecompatibilizer. That is, the resin molded article according to theexemplary embodiment has the same composition as the resin compositionaccording to the exemplary embodiment.

The resin molded article according to the exemplary embodiment may beobtained by preparing the resin composition according to the exemplaryembodiment and molding the resin composition, or may be obtained bypreparing a composition containing components other than the carbonfiber and mixing the composition with the carbon fiber during molding.

Examples of a molding method include injection molding, extrusionmolding, blow molding, hot press molding, calendering, coating molding,cast molding, dipping molding, vacuum molding, and transfer molding.

As the molding method of the resin molded article according to theexemplary embodiment, injection molding is preferable from the viewpointof obtaining a high degree of freedom for the shape.

The cylinder temperature during injection molding is, for example, from180° C. to 300° C. and preferably from 200° C. to 280° C. The moldtemperature during injection molding is, for example, from 30° C. to100° C. and preferably from 30° C. to 60° C.

The injection molding may be performed using a commercially availablemachine such as “NEX150” (manufactured by Nissei Plastic Industrial Co.,Ltd.), “NEX300” (manufactured by Nissei Plastic Industrial Co., Ltd.),SE50D (manufactured by Sumitomo Machinery Co., Ltd.), and the like.

The resin molded article according to the exemplary embodiment may beused in applications such as electronic and electric apparatuses,business machines, home electronics, automobile interior materials, andcontainers. Specific examples of the applications include: housings ofelectronic and electric apparatuses and home electronics; variouscomponents of electronic and electric apparatuses and home electronics,automobile interior components; storage cases of CD-ROM, DVD, and thelike; tableware; beverage bottles; food trays; wrapping materials;films; and sheets.

In particular, in the resin molded article according to the exemplaryembodiment, the carbon fiber is used as the reinforcing fiber, and thusthe mechanical strength and, particularly, elastic modulus are furthersuperior. Therefore, the resin molded article according to the exemplaryembodiment may be applied as an alternative to a metal component.

EXAMPLES

Hereinafter, the invention will be described in more detail usingExamples but is not limited to these examples.

Synthesis Example 1

Synthesis of PA-1

11.27 kg (97 mol) of hexamethylenediamine as a diamine component, 14.61kg (100 mol) of adipic acid (diamine component/dicarboxylic acidcomponent=0.97 (molar ratio)) as a dicarboxylic acid component, and 10 gof sodium hypophosphite and 18 kg of ion-exchanged water as a catalystare charged in a 50 liter autoclave. The autoclave is pressurized withN₂ from normal pressure to 0.05 MPa, released under pressure, andreturned to normal pressure. The operation is performed three times toperform N₂ substitution, and thereafter stirring is performed at 135° C.and 0.3 MPa to perform homogeneous dissolution. Thereafter, the solutionis continuously supplied by a liquid feed pump, the temperature israised to 240° C. in a heating pipe, and heat is applied for 1 hour.Thereafter, the reaction mixture is charged in a pressure reactionvessel, heated to 300° C. while maintaining the internal pressure of thevessel at 3 MPa to partially distill away water, thereby obtaining acondensate. Thereafter, the condensate is put into a hot water to bewashed, and then frozen with liquid nitrogen and pulverized with ahammer. The obtained resin powder is dried at 120° C. for 12 hours toobtain a polyamide resin PA-1 having an amino group at the terminal.

According to the method described above, when the terminal carboxy groupconcentration [B] is measured, the concentration is to be 0.27 mol/kg.In addition, when the terminal amino group concentration [A] ismeasured, [B]/([A]+[B]) is calculated, and the obtained value is 1.0.

Synthesis Example 2

Synthesis of PA-2

Polyamide PA-2 is obtained in the same manner as in Synthesis Example 1except that the amount of hexamethylenediamine is changed to 11.04 kg(95 mol) (diamine component/dicarboxylic acid component =0.95 (molarratio)).

According to the method described above, when the terminal carboxy groupconcentration [B] is measured, the concentration is to be 0.44 mol/kg.In addition, when the terminal amino group concentration [A] ismeasured, [B]/([A]+[B]) is calculated, and the obtained value is 1.0.

Synthesis Example 3

Synthesis of PA-3

Polyamide PA-3 is obtained in the same manner as in Synthesis Example 1except that the amount of hexamethylenediamine is changed to 11.51 kg(99 mol) (diamine component/dicarboxylic acid component =0.99 (molarratio)).

According to the method described above, when the terminal carboxy groupconcentration [B] is measured, the concentration is to be 0.09 mol/kg.In addition, when the terminal amino group concentration [A] ismeasured, [B]/([A]+[B]) is calculated, and the obtained value is 1.0.

Synthesis Example 4

Synthesis of PA-4

Polyamide PA-4 is obtained in the same manner as in Synthesis Example 1except that the amount of hexamethylenediamine is changed to 11.97 kg(103 mol) (diamine component/dicarboxylic acid component =1.03 (molarratio)).

According to the method described above, when the terminal carboxy groupconcentration [B] is measured, the concentration is to be 0 mol/kg. Inaddition, when the terminal amino group concentration [A] is measured,[B]/([A]+[B]) is calculated, and the obtained value is 0.0.

Synthesis Example 5

Synthesis of PA-5

Polyamide PA-5 is obtained in the same manner as in Synthesis Example 1except that the dicarboxylic acid component is changed to 14.61 kg (100mol) of adipic acid, and the diamine component is changed to 13.21 kg(97 mol) of metaxylene diamine (diamine component/dicarboxylic acidcomponent =0.97 (molar ratio)).

According to the method described above, when the terminal carboxy groupconcentration [B] is measured, the concentration is to be 0.24 mol/kg.In addition, when the terminal amino group concentration [A] ismeasured, [B]/([A]+[B]) is calculated, and the obtained value is 1.0.

Examples 1 to 15 and Comparative Examples 1 to 8 Pellets of a resincomposition are obtained by kneading components (numerical values in thetable represent the number of parts) shown in Tables 1 and 2 using atwin-screw extruder (TEM58SS, manufactured by Toshiba Machine Co., Ltd.)at a molten-kneading temperature (cylinder temperature) shown in thefollowing kneading conditions and Tables 1 and 2.

Regarding the fluidity of the obtained pellets, the MFR of the resincomposition is measured according to the method described above.Furthermore, the moldability of the obtained pellets is evaluated asfollows. The measurement results are shown in Tables 1 and 2.

Injection molding is performed out using a mold having a resin injectionport at the center part and a helical spiral groove starting from theinjection part, and the length of the injected resin is measured.

Spiral shape: width of 5 mm, thickness of 3 mm, and maximum flow lengthof 750 mm

Injection pressure: 100 MPa

Injection speed: 50 mm/s Evaluation criteria

A: Spiral flow length of 300 mm or more

B: Spiral flow length of 200 mm or more and less than 300 mm

C: Spiral flow length of less than 200 mm

The obtained pellets are baked at 600° C. for 2 hours, and the averagefiber length of the remaining carbon fibers is measured by the methoddescribed above. The measurement results are shown in Tables 1 and 2.

Kneading Conditions

Screw diameter: ϕ 58 mm

Rotation speed: 300 rpm

Discharge nozzle diameter: 1 mm

The obtained pellets are molded by an injection molding machine (NEX150,manufactured by Nissei Plastic Industrial Co., Ltd.) at an injectionmolding temperature (cylinder temperature) shown in Tables 1 and 2 and amold temperature of 50° C. to obtain D2 specimens (length of 60 mm,width of 60 mm, thickness of 2 mm).

Presence or Absence of Coating Layer

Using each of the obtained D2 specimens, the presence or absence of thecoating layer using the polyamide is determined in accordance with themethod described above.

TABLE 1 Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- ample ample ampleample ample ample ample ample ample ample ample Example 1 2 3 4 5 6 7 89 10 11 Compo- Thermoplastic Polypropylene 100 100 100 100 100 100 100100 100 100 sition Resin Polyethylene 100 Reinforcing Carbon Fiber 10 50100 200 10 200 10 200 200 10 Fiber A (Surface- treated) Carbon Fiber 5 B(not Surface- treated) Specific Aliphatic PA-1 20 60 80 100 10 100 15Resin PA PA-2 20 100 PA-4 5 PA-3 20 100 Aromatic PA-5 PA Ratio ofCarboxy Group 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.75 [B]/([A] + [B])Compatibilizer Maleic 5 10 30 50 5 50 5 50 2 5 Anhydride- modifiedPolypropylene Maleic 50 Anhydride- modified Polyethylene Total 135.0 220310 450 135 450 135 450 117 450 135 Con- Molten-kneading Temperature 260260 260 260 260 260 260 260 260 260 260 ditions (° C.) Injection MoldingTemperature 260 260 260 260 260 260 260 260 260 260 260 (° C.) Charac-MFR of Resin Composition 18 16 15 14 22 14 20 16 25 16 13 teristic (g/10min) Moldability of Resin Composition A A A A A A A A A A A. Presence orAbsence of Coating Pres- Pres- Pres- Pres- Pres- Pres- Pres- Pres- Pres-Pres- Pres- Layer ence ence ence ence ence ence ence ence ence ence enceAverage Fiber Length (mm) 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7Number of Parts of Carbon Fiber 10 50 100 200 10 200 10 200 5 200 10 (to100 Parts of Thermoplastic Resin) % by Weight of Specific Resin 200 12080 50 200 50 200 50 200 50 200 (to 100 Parts of Carbon Fiber) Number ofParts of Compatibilizer 25 16.7 38 50 25 50 25 50 20 50 25 (to 100 Partsof Specific Resin) Amount of Carbon Fiber occupied 7.4 22.7 32.3 44.47.4 44.4 7.4 44.4 4.3 44.4 7.4 in Resin Molded Article (%)

TABLE 2 Com- Com- Com- Com- Com- Com- Com- Com- par- par- par- par- par-par- par- par- ative ative ative ative ative ative ative ative Ex- Ex-Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- ample ample ample ample ampleample ample ample ample ample ample ample Example 12 13 14 15 1 2 3 4 56 7 8 Compo- Thermoplastic Polypropylene 100 100 100 100 100 100 100 100100 100 100 100 sition Resin Polyethylene Reinforcing Carbon Fiber 50 5050 10 50 10 50 10 25 Fiber A (Surface- treated) Carbon Fiber B (notSurface- treated) Specific Aliphatic PA-1 10 10 0.1 20 Resin PA PA-2 2548 2 PA-4 20 20 10 10 PA-3 25 2 48 Aromatic PA-5 20 PA Ratio of CarboxyGroup 1.0 1.0 1.0 1.0 0 0 0.5 0.5 [B]/([A] + [B]) Compatibilizer Maleic25 25 25 5 0.1 15 0.1 0.1 0.1 20 Anhydride- modified PolypropyleneMaleic Anhydride- modified Polyethylene Total 225 225 225 135 170.1 145170.1 130.1 100 100.2 140 125 Con- Molten-kneading Temperature 260 260260 260 260 260 260 260 220 260 260 220 ditions (° C.) Injection MoldingTemperature 260 260 260 260 260 260 260 260 220 260 260 220 (° C.)Charac- MFR of Resin Composition 16 18 14 19 4 6 10 12 16 16 14 8teristic (g/10 min) Moldability of Resin Composition A A A A C C C C B BC C Presence or Absence of Coating Pres- Pres- Pres- Pres- Pres- Pres-Pres- Pres- Ab- Ab- Ab- Ab- Layer ence ence ence ence ence ence enceence sence sence sence sence Average Fiber Length (mm) 0.7 0.7 0.7 0.70.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 Number of Parts of Carbon Fiber 50 50 5010 50 10 50 10 0 0 0 25 (to 100 Parts of Thermoplastic Resin) 100 100100 200 40 200 0 % by Weight of Specific Resin (to 100 Parts of CarbonFiber) Number of Parts of Compatibilizer 50 50 50 25 0.5 75 0.5 0.5 100100 (to 100 Parts of Specific Resin) Amount of Carbon Fiber occupied22.2 22.2 22.2 7.4 29.4 6.9 0.0 0.0 0.0 20.0 in Resin Molded Article (%)

The details of materials shown in Tables 1 and 2 are as follows.

Thermoplastic Resin

Polypropylene (NOVATEC (registered trade name) PPMA3, manufactured byJapan Polypropylene Corporation)

Polyethylene (ULTZEX 20100J, manufactured by Prime Polymer Co., Ltd.)

Reinforcing Fiber

Carbon fiber A (surface-treated, chopped carbon fiber TORAYCA(registered trade name), Toray Industries Inc., average fiber length 20mm, average diameter: 7 μm)

Carbon fiber B (not surface-treated, obtained after immersing the abovechopped carbon fiber TORAYCA (registered trade name), Toray IndustriesInc., in a solvent to remove a sizing agent)

Aliphatic PA (aliphatic polyamide)

-   -   PA-1 (PA-1 synthesized above)    -   PA-2 (PA-2 synthesized above)    -   PA-3 (PA-3 synthesized above)    -   PA-4 (PA-4 synthesized above)

Aromatic PA (aromatic polyamide)

-   -   PA-5 (PA-5 synthesized above)

Compatibilizer

Maleic anhydride-modified polypropylene (YOUMEX (registered trade name)110TS, manufactured by Sanyo Chemical Industries, Ltd.)

Maleic anhydride-modified polyethylene (MODIC M142 manufactured byMitsubishi Chemical Corporation)

From the above results, it is understood that a resin compositionsuperior in fluidity and moldability may be obtained in Examples ascompared to Comparative Examples.

When the molded articles prepared in each Example are analyzed by themethod described above, it is confirmed that a layer of thecompatibilizer used (layer of maleic anhydride modified polypropylene,layer of maleic anhydride modified polyethylene, and layer of maleicanhydride modified ethylene or vinyl acetate copolymer resin (EVA)) isinterposed between the coating layer and the thermoplastic resin (layerof the compatibilizer is formed on the surface of the coating layer).

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A resin composition comprising: a thermoplasticresin; a carbon fiber; a polyamide having at least one of a carboxygroup and an amino group at a terminal thereof, in which a presenceratio of the carboxy group present on the terminal (terminal carboxygroup) is higher than a presence ratio of the amino group present on theterminal (terminal amino group); and a compatibilizer.
 2. The resincomposition according to claim 1, wherein a relationship between apresence ratio of the terminal amino group and a presence ratio of thecarboxy group per 1 kg of the polyamide satisfies the following formula:0.6≤[B]/([A]+[B])≤1.0 wherein [A] represents a concentration of theterminal amino group (mol/kg) which is a molar amount of the terminalamino group per 1 kg of the polyamide, and [B] represents aconcentration of the terminal carboxy group (mol/kg) which is a molaramount of the terminal carboxy group per 1 kg of the polyamide.
 3. Theresin composition according to claim 1, wherein the thermoplastic resinis a polyolefin.
 4. The resin composition according to claim 1, whereinthe compatibilizer is a modified polyolefin.
 5. The resin compositionaccording to claim 1, wherein an average fiber length of the carbonfibers is from about 0.1 mm to about 5.0 mm.
 6. The resin compositionaccording to claim 1, wherein a content of the carbon fiber is fromabout 0.1 parts by weight to about 200 parts by weight with respect to100 parts by weight of the thermoplastic resin.
 7. The resin compositionaccording to claim 1, wherein a content of the compatibilizer is fromabout 1 parts by weight to about 50 parts by weight with respect to 100parts by weight of the polyamide.
 8. The resin composition according toclaim 1, wherein a content of the polyamide is from about 0.1% by weightto about 200% by weight with respect to a weight of the carbon fiber. 9.A resin molded article comprising: a thermoplastic resin; a carbonfiber; a polyamide having at least one of a carboxy group and an aminogroup at a terminal thereof, in which a presence ratio of the carboxygroup present on the terminal (terminal carboxy group) is higher than apresence ratio of the amino group present on the terminal (terminalamino group); and a compatibilizer.
 10. The resin molded articleaccording to claim 9, wherein a relationship between a presence ratio ofthe terminal amino group and a presence ratio of the carboxy group per 1kg of the polyamide satisfies the following formula:0.6≤[B]/([A]+[B])≤1.0 wherein [A] represents a concentration of theterminal amino group (mol/kg) which is a molar amount of the terminalamino group per 1 kg of the polyamide, and [B] represents aconcentration of the terminal carboxy group (mol/kg) which is a molaramount of the terminal carboxy group per 1 kg of the polyamide.
 11. Theresin molded article according to claim 9, wherein the thermoplasticresin is a polyolefin.
 12. The resin molded article according to claim9, wherein the compatibilizer is a modified polyolefin.
 13. The resinmolded article according to claim 9, wherein an average fiber length ofthe carbon fibers is from about 0.1 mm to about 5.0 mm.
 14. The resinmolded article according to claim 9, wherein a content of the carbonfiber is from about 0.1 parts by weight to about 200 parts by weightwith respect to 100 parts by weight of the thermoplastic resin.
 15. Theresin molded article according to claim 9, wherein a content of thecompatibilizer is from about 1 part by weight to about 50 parts byweight with respect to 100 parts by weight of the polyamide.
 16. Theresin molded article according to claim 9, wherein a content of thepolyamide is from about 0.1% by weight to about 200% by weight withrespect to a weight of the carbon fiber.